The acquisition and reproduction of audio signals was among the first applications of electronic circuits. Nowadays, audio electronics are ubiquitous and can be found in television and hifi-stereo sets, car audio systems and more recently in cellular phones and many other portable applications. The vast majority of these electronics is in the form of integrated circuits. Audio amplifier systems may be used in mobile phones and other mobile devices. An example audio amplifier system also referred to as a smart speaker driver maximizes acoustic output while ensuring that the speaker is not damaged. This is done by predicting the membrane excursion and estimating the voice-coil temperature by means of a speaker model. The membrane excursion is directly related to sound pressure level. Differences between the speaker model and the real world are eliminated by feeding back real-time measurement of the current going into the speaker.
The heart of the smart speaker driver is a high efficiency class-D amplifier that drives the actual loudspeaker. The amplifier is supplied by a DC-DC boost converter that guarantees high output power even at low battery voltage. The DC-DC boost converter is controlled from the digital domain and is only enabled when high power is needed at the amplifier output. The combined efficiency of the DC-DC boost converter and amplifier is optimized by doing a coarse envelope tracking of the audio signal.